The soles of one's feet, together with the vestibular system of one's inner ear, provide cues about self-motion. The central nervous system processes these motion cues, together with those provided by the feet, vestibular system, and other body parts to estimate self-motion in 6 degrees of freedom: three of which are angular and three of which are linear.
In some cases, injury, disease, or prolonged exposure to altered gravity disrupts the flow of sensory information, resulting in dizziness, blurred vision, inability to orient correctly (including the ability to align with the vertical), and reduced ability to stand or walk.
Balance prostheses have been developed in an effort to improve postural stability in the balance impaired. Uses for balance prostheses include: (1) a balance “pacemaker” to reduce dizziness and imbalance due to abnormal fluctuations in the peripheral vestibular system, (2) permanent replacement of vestibular or balance function, (3) temporary replacement of motion cues that commonly occur following ablative surgery of the inner ear, and (4) vestibular/balance rehabilitation.
Balance prostheses may be implantable or non-implantable. An implantable prosthesis delivers self-motion cues to the central nervous system via implanted stimulators. Non-implantable prostheses are a less invasive means of providing some self-motion cues. Such prostheses operate by, for example, stimulating the vestibular nerve via surface electrodes or by displaying self-motion cues using “sensory substitution” (e.g., acoustic inputs or electric currents applied to the tongue). (See P. Bach-y-Rita, “Late post-acute neurologic rehabilitation: neuroscience, engineering and clinical programs,” Arch Phys. Med. Rehab, Vol. in press, 2002, and P. Bach-y-Rita, K. A. Kaczmarek, et al., “Form perception with a 49-point electrotactile stimulus array on the tongue: a technical note,” J Rehabil Res Dev, Vol. 35, No. 4, 1998, p. 427-30.) Stimulation using auditory cues is described in U.S. Pat. No. 5,919,149 (“the '149 patent”), the full disclosure of which is incorporated by reference herein.
U.S. Pat. No. 6,546,291, the full disclosure of which is incorporated herein by reference, describes vestibular prostheses that include tactile vibrators (tactors) mounted on the subject's torso.